Monitoring systems for detecting potential fire conditions in commercial or industrial buildings are often distributed throughout the various floors or areas of the respective building. Detector or control units are placed at locations on various floors or in devices where it is desirable to be able to determine, as early as possible, whether or not there is a potential fire condition.
The detectors or control devices are conventionally linked by one or more sets of communications lines to a common control panel. This control panel receives information from the spaced apart detectors or control devices and is often equipped to make a determination as to whether or not one or more of the detectors is reporting a potential fire condition.
One form of communication system and method are disclosed in Tice et al. U.S. Pat. No. 4,916,432 entitled "Smoke and Fire Detection System Communication" assigned to the assignee of the present invention. Systems of the type of the noted Tice et al. patent provide discrete time intervals during which electrical energy can be supplied to the remote units via the communication links and the common control panel. Using the communication link to also power the displaced detectors, control devices, as well as other units in the system, minimizes the number of lines which need to be installed to service the displaced units.
In known communication systems, the length of time available to provide electrical energy to the displaced units can become a significant issue. As the number of detectors or other units increases, the amount of electrical energy which needs to be supplied through the communications link also increases.
The communication links, which may be several thousand feet long, are often implemented with relatively small diameter wire, for example, 18 gauge. The length and size of the wire limit the amount of electrical energy which can be supplied in a given time interval. Further, as the number of detectors or control units increases, the length of the communication lines may also increase. This results in additional losses which may make it impossible to adequately power the detectors or other units which are located furthest away from the common control element.
Additional difficulties which can be experienced as the number of detectors on a communication loop is increased, can include electrical noise which interferes with an ability to properly detect information being transmitted to or being received from detectors or control units.
There thus continues to be an unmet need for communication systems which can provide sufficient quantities of energy to support larger numbers of detectors than has heretofore been possible. In addition, it would be desirable to be able to increase the noise immunity of such systems notwithstanding the fact that even longer wire lengths and larger numbers of detectors need to be installed to meet the needs of current building requirements.
Preferably, providing for increased energy levels as well as increased noise immunity can be achieved without substantially increasing either the cost of such systems or the complexity thereof. It would also be desirable to be able to provide for larger peak to peak voltages of information from distributed units to the common control element so as to provide increased noise immunity and reliability in such systems.